HSC Biology 2024

(a) [2 marks]. Pollen is in the anther; ovules are in the ovary.

(b) [3 marks].

Marker's note. Name the structures shown (anther, ovary - not stamen or pistil) and use specific organisms ("yeast" not "fungi"). Self-pollination is still sexual; external fertilisation (e.g. fish) is still sexual.

(a) [2 marks]. Wear disposable gloves. This stops microbes in the samples contacting the skin, preventing pathogens entering through cuts or being transferred to the mouth, so the risk of infection is reduced.

(b) [2 marks]. Repeat the test. Culture several plates (e.g. five) from the same sample under identical conditions; similar results across the replicates show the data are reliable, and any odd plate is an outlier.

Marker's note. The justification must add reasoning beyond the question stem ("prevents contact with microbes and entry through the skin", not just "prevents infection"). Keep reliability, validity and accuracy distinct.

[2 marks]. Ultraviolet (UV) radiation is absorbed by DNA and can bond adjacent thymine bases into thymine dimers, altering the base sequence. If this happens in the DNA of gametes (sex cells), the change can be inherited, making it a germline mutation. (X-rays or gamma rays are also acceptable.)

Marker's note. Distinguish germline (gametes, heritable) from somatic (body cells, not inherited), and name a radiation that genuinely damages DNA.

(a) [2 marks]. Melanoma (skin cancer) is caused by excessive UV radiation in sunlight. UV is absorbed by DNA in skin cells and causes mutations in genes controlling cell division; accumulated mutations can lead to uncontrolled division and a tumour.

(b) [3 marks]. A campaign such as "Slip, Slop, Slap" teaches that UV damages skin-cell DNA and that covering up, sunscreen and shade reduce exposure. Raising awareness of the cause and the protective behaviours increases the proportion of people using sun protection, so fewer people accumulate UV damage and the incidence of melanoma falls over time.

Marker's note. Name a disease genuinely caused by environmental exposure; give a cause, not a symptom; and link the program's features to a behaviour change and then to reduced incidence.

(a) [2 marks]. Jack lost his eye through injury, not a change to his DNA. His genome still carried the instructions for two eyes, and cloning copies the nuclear DNA, so the clone inherited the unaltered code. The injury was an acquired, non-heritable change.

(b) [4 marks]. By somatic cell nuclear transfer (SCNT):

1. Remove the nucleus from a donor egg (enucleation).
2. Take the nucleus (full genome) from a body cell of the animal to be cloned.
3. Insert that nucleus into the enucleated egg.
4. Stimulate the egg, usually with an electric current, to divide like a zygote.
5. Implant the embryo into a surrogate mother.
6. The surrogate gives birth to a clone genetically identical to the nucleus donor.

Marker's note. In (a), tie the unaltered genome to the two-eyed outcome. In (b), give the SCNT steps in sequence, including enucleation, electrical stimulation and the surrogate.

[4 marks]. Wheat stem rust (fungus Puccinia graminis) infects wheat, producing reddish-brown pustules of spores on stems and leaves. These rupture the surface, reduce photosynthesis and weaken the stem so plants lodge (fall over). The result is shrivelled, poor-quality grain and much lower yield, causing major economic losses for farmers. (Other named diseases such as stone-fruit scab or potato blight are equally acceptable.)

Marker's note. Name a specific plant disease, describe its signs, and give a directional effect on production (reduced yield or quality), not just "it has an impact".

[5 marks]. Outbreaks linked to raw milk were high and variable early on (around 50 to 70) but fell sharply after about 1945 to fewer than 10, while outbreaks linked to pasteurised milk stayed consistently low (under 5) throughout.

Pasteur disproved spontaneous generation, showing microbes already present in a substance cause disease, and that heating kills most of them. Pasteurisation applies this: heating milk to about 70 degrees C kills the bacteria that cause milk-borne disease, which is why pasteurised milk produced so few outbreaks. The steep fall in raw-milk outbreaks after 1945 reflects wider pasteurisation and fewer people drinking raw milk; the few pasteurised-milk outbreaks come from failures in heating, storage or transport.

Marker's note. Quote specific data and a date ("after 1945, raw-milk outbreaks fell from about 50 to under 10") and connect Pasteur's findings directly to the trends.

(a) [3 marks]. Both parents are carriers, Rr. The cross Rr x Rr:

Ratio 1 RR : 2 Rr : 1 rr. Only rr has cystic fibrosis, so the probability is 1/4 = 25% (independent of the first child).

(b) [4 marks]. Each amino acid is coded by a three-base codon. The three deleted nucleotides span the boundary between the isoleucine (507) and phenylalanine (508) codons. Removing exactly three bases keeps the reading frame (no frameshift), but the remaining bases re-form a codon that still codes for isoleucine, because the code is degenerate (AUC and AUU both code for isoleucine). So isoleucine is still made, but the phenylalanine codon is lost, removing only that one amino acid.

Marker's note. State the probability in one consistent form (not 1/4 and 33%). In (b), use the chart to show the deletion spans two codons yet, by degeneracy, the remaining triplet still codes for isoleucine.

(a) [2 marks]. Plot (1990, 3.1), (2000, 3.7), (2010, 4.3), (2020, 5.6) with percentage on the y-axis and year on the x-axis, then draw one straight line of best fit balancing the points. The trend is a steady rise.

(b) [3 marks]. Extrapolating the line to 2040 gives about 7%.

So about 630 million people. (A reading of 6 to 7%, giving roughly 540 to 630 million, is acceptable from a reasonable line.)

Marker's note. Plot accurately, draw a balanced line of best fit, show the extrapolation on the graph, and show the percentage calculation with the large number.

(a) [3 marks]. Process A is transcription.

• Similarity: both unwind the DNA and build a new strand by complementary base pairing against a template.
• Differences: replication copies the whole molecule into two double-stranded DNA molecules using DNA polymerase (A with T); transcription copies one gene into single-stranded mRNA using RNA polymerase (A with U). Replication happens once before division; transcription happens whenever a gene is expressed.

(b) [5 marks].

• mRNA is transcribed from the DNA template in the nucleus and carries the message, as a sequence of codons, to a ribosome. Its codon order sets the amino acid order, so it is the template for translation.
• tRNA has an anticodon at one end and a specific amino acid at the other. At the ribosome each anticodon pairs with the complementary mRNA codon, delivering the right amino acid in the right order.
• Together: as the ribosome moves along the mRNA, successive tRNAs add their amino acids and peptide bonds form, building a polypeptide whose sequence is set by the mRNA. Without mRNA there is no template; without tRNA the amino acids cannot be matched to codons.

Marker's note. In (a) compare the same feature for both (product, enzyme, T versus U). In (b) use correct terms (codon, anticodon, complementary) and link mRNA and tRNA to building the polypeptide.

(a) [1 mark]

4 am.

(b) [3 marks]

The kookaburra displayed torpor: its temperature fell from about 39 degrees C in the evening to a low near 4 am before rising - a significant drop in physiological activity. The human did not: its temperature stayed near 37 degrees C throughout, showing tight homeostatic control.

(c) [2 marks]

The kookaburra can fluff up its feathers, trapping insulating air to reduce heat loss; with shivering (muscle contractions that release heat), this raises its body temperature.

Marker's note. Read the x-axis carefully in (a). In (b) name the organism and justify with specific temperatures and times. In (c) give an adaptation that genuinely generates or retains heat.

[7 marks]

The body responds first with innate, then adaptive immunity.

Innate (rapid, non-specific)

damaged cells and bacteria release chemicals (e.g. histamine) that trigger inflammation. Blood vessels dilate and become leaky, bringing phagocytes (neutrophils and macrophages) that engulf the bacteria by phagocytosis.

Adaptive (slower, specific)

macrophages present H. pylori antigens to helper T cells, which release cytokines that activate the specific response:

• B cells become plasma cells that secrete antibodies, neutralising the bacteria and tagging them for phagocytes.
• Cytotoxic T cells destroy infected cells.
• Memory B and T cells remain for a faster secondary response.

Together the innate response gives immediate defence and the adaptive response gives specific, long-lasting immunity to clear H. pylori.

Marker's note. Structure the answer around the lines of defence, show innate and adaptive working together, and use the stimulus (gut lining, inflammatory cells).

(a) [2 marks]. Crossing over swaps segments between homologous chromosomes, making new allele combinations. This increases genetic variation in the gametes and offspring, giving the population a better chance of surviving environmental change.

(b) [2 marks]. Four single chromosomes (two parental, two recombinant), using the loci D/d, E/e, H/h shown:

• Parental: D E H
• Parental: d e h
• Recombinant: D E h
• Recombinant: d e H

Each gamete gets one single chromosome; the recombinants show the swapped alleles. (Exact recombinant alleles depend on the crossover point in the diagram.)

Marker's note. In (a) link crossing over to variation, then to survival. In (b) draw single chromosomes (not pairs) with alleles at the correct loci; distinguish chromosomes from chromatids.

[7 marks].

1. Recombinant DNA technology (GM crops, e.g. Bt cotton). A bacterial insecticidal gene is inserted so the crop makes its own pest protection.

• Impact: higher yields and less chemical insecticide, lowering costs and increasing food supply.
• Ethics: the seeds are patented and bought each season, so farmers cannot save seed - this disadvantages poorer farmers and concentrates control with a few companies, raising equity concerns.

2. Selective breeding and hybridisation (e.g. high-yield dairy cattle). Animals with desired traits are bred over generations.

• Impact: greater milk yields and cheaper food for consumers and farmers.
• Ethics: intense selection for one trait has reduced fertility and caused welfare problems, and lowers genetic diversity, making herds more disease-prone.

Both offer real benefits (more food, higher yields, lower cost) but raise genuine ethical concerns - equity and corporate control, and animal welfare - that society must weigh.

Marker's note. Pick two genuine biotechnologies with specific examples; for each link a clear impact to a specific ethical implication, and discuss (weigh) rather than list.

[5 marks]. How they work: a cochlear implant is used when the cochlea's hair cells are damaged. A microphone and processor convert sound to electrical signals sent to electrodes in the cochlea, which bypass the damaged hair cells and directly stimulate the auditory nerve, carrying the signal to the brain.

Effect (with the data): age at implantation matters. Implanted young, children sharply reduce sign language (only about 10% still use it five years later), shifting to spoken communication. Implanted at three to five years, they reduce sign language less. Implanted over five years, they keep using sign language and change little. So implants shift children toward spoken communication most when fitted younger.

Marker's note. Say the implant directly stimulates the auditory nerve (bypassing the cochlea) and refer to the data for every age group, comparing the trends.